The present invention relates to circuits for determining the direction and position of a magnetic tape, and more particularly to a tape remaining circuit which provides a numeric value, in equal increments of the time remaining, corresponding to the amount of tape remaining on a supply reel.
Typical of end-of-tape circuits for determining the direction and amount of tape on the supply reel of, for example, a video production recorder, are those systems which determine the tape remaining by comparing the rotation rate of the reel to the rotation rate of the capstan or tape timer tachs. Typically, the number of capstan tach pulses are counted during a selected reel tach period. The value of capstan tach counts then are averaged over several reel tach periods to average out and thus minimize, errors caused, for example, by tension arm movement. The time required to perform the integration is relatively large, i.e., several seconds, and therefore present end-of-tape circuits take a like amount of time to provide a valid tape remaining value. This is particulary disadvantageous when the direction of tape is reversed, particularly towards the end of the tape. That is, the failure to provide a valid tape remaining value during a few reel rotations, can allow the tape to run off the reel.
The present invention overcomes the shortcomings of previous mention by providing a tape remaining circuit which minimizes integration time, while compensating for perturbations due to tension arm movement, thereby rapidly providing valid indication of the exact position and direction of a magnetic tape. To this end, the number of capstan tach or tape timer tach pulses are counted during a reel tach period. The tension arm position is sensed and any change of position thereof is added as a correction factor to the capstan tach or tape timer tach count. The combined count provides a corrected capstan or tape timer count which no longer contains a tension arm error. The circuit instantly minimizes errors due to tension arm position and thus reduces the time required for integration or averaging. In a modification, the output is further modified to provide a linearized signal that produces a numeric value equal to a given length of tape remaining, i.e., which compensates for the squaring effects of the radius of the reel.
Accordingly, it is an object of the invention to determine rapidly the tape remaining on a supply reel.
It is another object to provide a circuit for sensing the direction and position of a tape with a minimum of integration time.
It is a further object to sense a change in the position of a tension arm and instantly provide a tape remaining value which compensates for variation in the tension arm position.
Another object is to provide a linearized signal as a numeric value equal to a given length of tape remaining on a reel.